1. Field of the Invention
The present invention relates to an elastic shaft joint which is assembled into a universal joint for constituting, for example, a steering apparatus for a car so as to transmit a motion of a steering wheel to a steering gear and to prevent a vibration on the side of the steering gear from being transmitted to the steering wheel.
2. Related Background Art
A steering apparatus for a car is arranged to transmit a motion of a steering shaft which is rotated by a steering wheel to a steering gear so as to give a steering angle to the wheels. Normally, the steering shaft and the input shaft of the steering gear can not be disposed on the same straight line. For this reason, a universal joint is arranged between the steering shaft and the input shaft to transmit a motion of the steering wheel to the steering gear. A vibration absorbing ability is conventionally given to the universal joint, in order to prevent the vibration which is transmitted from the wheels to the steering gear when the car is run from further being transmitted to the steering wheel to give unpleasant feeling to the driver. In order to give the vibration absorbing capability to the universal joint in this manner, an elastic material such as rubber is usually assembled into this universal joint so that the transmission of the vibration is prevented by use of the elastic material.
As such an elastic shaft joint or a universal joint assembling such elastic shaft joint therein, there are conventionally known joints disclosed in Japanese Patent Application Laid-Open Nos. 56-39325 (French Patent Application Laid-Open No. 2464404), 56-131831, 60-184716 to 60-184718, 60-215122, and 60-215123, 61-201924, Japanese Utility Model Application Laid-Open Nos. 54-82257, 5-83462, and 5-89964, French Patent Application Laid-Open No. 2614985, U.S. Pat. No. 4,509,775, etc.
In the elastic shaft joint conventionally known, leaving the case in which a vibration in the direction of rotation of the shaft such as a steering shaft is applied, when a vibration in the axial direction of this shaft is applied, the capacity of the shaft joint to attenuate this vibration is poor, so that the vibration in the axial direction is easily transmitted to the steering wheel. Especially, when a displacement along the axial direction is applied to a part with a shaft mounted thereon, for example, when the distance between the steering gear and the front end portion of the steering shaft is changed due to a vibration upon running of the car, this displacement can not be absorbed. Also, if it is required to absorb a tolerance in manufacturing or assembling the parts when the elastic shaft joint is to be assembled into a steering apparatus of the car, such requirement can not be satisfied. Further, when one end portion of the shaft with the elastic shaft joint assembled therein is inserted in the base end portion of a yoke of a universal joint in the axial direction thereof, this end portion of the shaft is required to be displaced in the axial direction, which also can not be satisfied.
Taking these circumstances into account, such a structure as disclosed in, for example, Japanese Patent Application Laid-Open No. 11-048991 is contrived in which a shaft is divided into a pair of elements and the paired. elements are brought into serration engagement with each other at a coupling portion thereof. Since the portion of the serration engagement between the paired elements allows a large displacement in the axial direction, even when a displacement in the axial direction is applied onto a portion with the shaft mounted thereon upon running of the car, this displacement is absorbed. If a tolerance in manufacturing or assembling of the parts is required to be absorbed when the elastic shaft joint is to be assembled into the steering apparatus of the car, it is possible to prevent such tolerance. Further, when one end portion of the shaft with the elastic shaft joint mounted thereon is to be inserted into the base end portion of the yoke of the universal joint in the axial direction, it is possible to displace this end portion of the shaft in the axial direction.
However, the cost is inevitably increased when the serration engagement portion is provided in a part of the shaft. That is, in order to prevent a backlash of the serration engagement portion, irrespective of presence or absence of vibration in running, it is required to form a slit on the side of an outer shaft on which a highly accurate processing is performed or a female serration is formed, for elastically expanding or contracting the diameter of this outer shaft. Further, it is required to provide a member for elastically contracting the diameter of the outer shaft.